Aluminum alloy for galvanic anodes



April 4, 1967 CURRENT DENSITY TAKESHI SAKANO ETAL 3,312,545

ALUMINUM ALLOY FOR GALVANIC ANODES Filed Aug. 31, 1964 L0 IO Hr HOUR) K TWQ,

71 INVENTORS BY W65. M

United States Patent ALUMlNUM ALLOY FOR GALVANIC ANODES Takeshi Sakano, Moto-machi, and Kazuo Toda, Nakamachi, Japan, assignors to Mitsubishi Kinzolru Kogyo Kabushiki Kaisha, Tokyo-t0, Japan, a joint-stock company of Japan Fiied Aug. 31, 1964, Ser. No. 393,224 Claims priority, application Japan, Sept. 6, 1963, 38/ 46,692 9 Claims. (Cl. 75-146) This invention relates to an improved aluminum alloy for galvanic anodes and has, as one of its objects, that of improving the characteristics of the aluminum alloy disclosed in U.S. patent application Ser. No. 261,- 519 filed on Feb. 27, 1963, now Patent No. 3,172,760.

In patent application No. 29,639/1962, there is disclosed an aluminum alloy for galvanic anodes which is characterized by a content of from 0.005% to 0.1% of indium and from 0.5% to of Zinc. For example, the anode potential of an aluminum alloy consisting of aluminum of commercial grade purity, 0.02% of indium, and 2.5% of Zinc is, in seawater, 1.10 volt (all electrical potentials mentioned in the present specification being values referred to as a saturated calomel electrode) and its galvanic current efficiency is as high as 70%- 85%, although it varies depending upon the operating condition.

This invention has resulted from research conducted to further improve the characteristics of the aluminum high as 80%85%. Thus, it will be clear that this invention provides an excellent galvanic anode material. The' effective amount of cadmium to be added ranges from 0.005% to 0.1%. Addition of cadmium of less than 0.005% has little effect in improving the galvanic dissolving state of anode, whereas addition of cadmium of an amount ranging from 0.1% to 0.5% has a tendency to decrease the current etliciency and impair the galvanic dissolving state. Accordingly, the preferable range of the amount of addition of cadmium was found to be from 0.005% to 0.1%, and the amount of addition of cadmium in this range greatly improves the performance characteristics of the anode. Thus, the characteristic feature of the aluminum alloy of this invention is that it contains from 0.005% to 0.1% of indium, from 0.5% to 20% of zinc, and in addition from 0.005% to 0.1% of cadmium.

This invention can be more fully understood from the following description, reference being made to the accompanying drawing in which a single figure represents curves showing comparison between galvanic characteristics of an anode made of aluminum alloy of this invention and that made of the alloy according to the patent application No. 29,639/1962.

The following specific examples are given by way of illustration, and are not to be considered as limiting in any way the scope and spirit of the invention. All parts are by weight throughout the specification and claim.

Example 1 This example illustrates the results of tests to compare the galvanic characteristics of anodes employing the aluminum alloys embodying this invention and those of the patent application No. 29,639/ 1962. Table I below shows the compositions of various aluminum alloys, anode potentials, and galvanic current efficiencies (currents were passed through synthetic sea water at an anodic current density of 1 ma./cm.

TABLE I Potential after 500 Galvanic Sample number Composition of alloy hours of galvanic current action (volt) efficiency (percent) 1 (this invention) 99.85% Al; Zn, 2.5%; In, 0.02%; Cd, 0.005% -1.12 v. (SCE) 85 2 (this invention) 99.85% Al; Z 2.57' I 0.02%; Cd, 0 1.125 v. (SOE). 85 3 (this invention) 99 85% Al; Zn .5 0. 84 4 (this invention) 5 0. 84 5 (this invention). 5 0. 83 6 (this invention) .0 so 7 (this invention) 99.85% A 84 8 (this invention) 99.85% A 80 9 99.85% Al 84 99.85% A 83 99.85% A 70 tion No. 29,639/1962 exhibits uniform dissolving state throughout its surface under current conducting condition, at low current density conditions, there is a tendency for the aluminum hydroxide that has been formed by the dissolving of aluminum to adhere to a portion of the aluminum anode effiux surface so that the area of active anodic surface is decreased to decrease the current generated and hence the current efficiency. Addition of a small amount of cadmium in accordance with this invention effectively prevents aluminum hydroxide from depositing on the anode surface, this always maintaining the active anodic surface. As a result, attenuation of the current generated is very slight, and the performance characteristic becomes stable, thus increasing the galvanic current eiiiciency to a value as Example 2 This example shows a comparison between an aluminum alloy anode of this invention and that of patent application No. 29,639/ 1962 in terms of natural galvanic action.

Both samples were arranged to conduct current in synthetic sea water contained in the same tank. The

eflective area of the sample was 10 cm. circuit resistance was 50, and measurement of the current generated was made by measuring the voltage drop across a standard resistor of 0.019. i

TABLE II Amount of current Ration of Anode Sample number Composition of alloy generated after 500 current potential hours of galvanic action generated 1 (this invention) 99.85% Al; Zn, 2.5%; In, 0.02%; Cd, 0.01% 1 12 ma. (1.2 ma./cin. 2. 4 -1.11v. 2 99.85% Al; Zn, 2.5%; In, 0.02% I 5 ma. (0.5 Ina cm. 1 -1.10 v

The accompanying drawing illustrates the characteristics of these two alloy anodes wherein curve 1 is a plot of current generated by the alloy anode of this invention and curve 2 is that of the alloy anode accord ing to patent application No. 29,639/ 1962. As can be clearly observed from the result of this comparison test, value of current generated by the alloy anode of this invention is about 2.4 times larger than that of the invention disclosed in the reference patent application which means that improved solubility and sustaining of low potential greatly contribute to the improvement in the anode characteristics. Thus, the alloy anode of this invention has far superior corrosion protective property than the alloy anode according to patent ap plication No. 29,639/ 1962 which is a very important merit. 7

While the invention has been explained by describing particular embodiments thereof, it will be apparent that improvement and modifications may be made without departing from the scope of the invention as defined in the appended claims,

What is claimed is:

1. An aluminum alloy for galvanic anodes consisting essentially of 0.005% to 0.1% Of indium, 0.5% to 20% of zinc, 0.005% to 0.1% of cadmium, and balance be ing aluminum, all percentages being by weight.

2. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 2.5%, indium 0.02%, and cadmium 0.01%, all percentages being by weight.

4. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 2.5%, indium 0.02%, and cadmium 0.05%.

5. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 2.5 indium 0.02%, and cadmium 0.1%.

6. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 0.5%, indium 0.02%, and cadmium 0.01%.

7. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 20%, indium 0.02%, and cadmium 0.01%.

8. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 2.5%, indium 0.005% and cadmium 0.01%.

9. An aluminum alloy for galvanic anode as defined in claim 1, wherein the specific content of zinc is 2.5%, indium 0.09% and cadmium 0.01%.

References Cited by the Examiner UNITED STATES PATENTS 1,117,308 11/1914 Bayliss et al. 75146 1,658,702 2/1928 Bonhoett 75-138 1,997,165 4/1935 Brown 75-138 3,227,644 1/ 1966 Rutemiller 75146 DAVID L. RECK, Primary Examiner.

R. O. DEAN, Assistant Examiner. 

1. AN ALUMINUM ALLOY FOR GALVANIC ANODES CONSISTING ESSENTIALLY OF 0.005% TO 0.1% OF INDIUM, 0.5% TO 20% OF ZINC, 0.005% TO 0.1% OF CADMIUM, AND BALANCE BEING ALUMINUM, ALL PERCENTAGES BEING BY WEIGHT. 